The present invention relates to a light-sensitive composition and in particular to a light-sensitive composition suitably used for preparing a presensitized plate for use in making a lithographic printing plate (hereinafter referred to as "PS plate"). More specifically, the present invention relates to a light-sensitive composition which has a sufficient ability Of being developed with a so-called exhausted developer which comprises a large amount of components of light-sensitive layers dissolved therein and which can provide a lithographic printing plate having excellent printing durability and having excellent ink-receptivity during printing even after storing the lithographic printing-plate under high temperature and humidity conditions or after exposing the lithographic printing plate to indoor-light such as a fluorescent lamp.
As light-sensitive layers for so-called negative-working PS plates whose portion exposed to light is hardened through irradiation with actinic light rays, there have been known a so-called alkali-developable light-sensitive layer as disclosed in Japanese Patent Publication for Opposition Purpose (hereinafter referred to as "J.P. KOKOKU") No. Sho 55-34929(=U.S. Pat. No. 4,123,276) in which the unexposed portion is removed through development with an aqueous alkaline developer and a so-called solvent-developable light-sensitive layer as disclosed in Japanese Unexamined Patent Publication (hereinafter referred to as "J.P. KOKAI") No. Sho 56-94346(=U.S. Pat. No. 4,337,307) in which the unexposed portion is removed through development with a developer mainly comprising an organic solvent. However, the use of the alkali-developable light-sensitive layer has been the leading mainstream in this field from the viewpoint of industrial safety and health. The majority of these alkali-developable light-sensitive layers comprise combinations of diazonium compounds as light-sensitive substances and polymer binders and the alkali-developability of these light-sensitive layers is mainly determined by the properties of these polymer binders used. In general, if the alkali-developability is imparted to binders, the wear resistance of the polymers are deteriorated and accordingly the resulting lithographic printing plate has insufficient printing durability. To solve these problems, there have been proposed the use of alkali-soluble polyurethane resins as disclosed in U.S. Pat. No.4,983,491 and J.P. KOKAI Nos. Hei 1-293336 and Sho 63-136039 and these urethane polymers permit the production of PS plates which simultaneously satisfy these requirements of both alkali-developability and high printing durability. However, it has been required that these PS plates are sufficiently developable with not only fresh developers free of any component of the light-sensitive layers, but also so-called exhausted developers which are obtained after development of a large amount of PS plates and which accordingly comprise a large amount of unexposed portions of light-sensitive layers dissolved therein. Moreover, it has also been desired that a large amount of the resulting PS plates can be processed with a constant amount of a developer or that the resulting PS plates have improved developability, from the viewpoint of saving natural resources. There has thus been desired for further enhancement of alkali-developability of these PS plates.
On the other hand, the ink-receptivity of PS plates is important in addition to the foregoing developability and printing durability and there has been proposed, for instance, a method for improving ink-receptivity which comprises adding a polymer compound as disclosed in U.S. Pat. Nos. 4,294,905 and 4,902,602. However, the lithographic printing plates obtained after plate-making processes of these PS plates undergo deterioration of the ink-receptivity when they are stored under high temperature and humidity conditions or exposed to light. Thus, there has been desired for further improvement of the ink-receptivity. In addition, J.P. KOKAI No. Sho 63-136039 discloses a light-sensitive composition which is alkali-developable and has improved printing durability and ink-receptivity and which comprises a combination of a diazo resin, a polyurethane resin having carboxyl groups and/or a modified polyvinyl acetal resin having substituents carrying acidic hydrogen atoms and a fluorine atom-containing surfactant. However, the polymer binder used in the light-sensitive composition does not provide a PS plate capable of being developed with an exhausted developer and further the PS plate obtained from such a light-sensitive composition cannot provide, after a plate-making process, a lithographic printing plate having sufficient ink-receptivity. In other words, the ink-receptivity of the lithographic printing plate is insufficient when it is stored under high temperature and humidity conditions and the portions thereof exposed to light have low ink-receptivity.